1. Field of the Invention
The invention relates to a hybrid vehicle and, more particularly, to a hybrid vehicle that is provided with an internal combustion engine, an electric power storage device, and an electric motor which generates a traveling driving force by receiving electric power supply from the electric power storage device.
2. Description of Related Art
Japanese Patent Application Publication No. 2013-252853 (JP 2013-252853 A) discloses a hybrid vehicle that has a charge depleting (CD) mode and a charge sustaining (CS) mode. The CD mode is a mode in which a state of charge (SOC) of an electric power storage device is actively consumed by EV traveling being proactively performed while HV traveling is allowed. The CS mode is a mode in which the SOC is controlled within a predetermined range based on an appropriate switching between the HV traveling and the EV traveling. During the EV traveling, traveling is performed by the use of a motor generator alone with an engine stopped. During the HV traveling, traveling is performed with the engine in operation. Also disclosed is a threshold of power for starting the engine higher in the CD mode than in the CS mode (refer to JP 2013-252853 A).
In the hybrid vehicle disclosed in JP 2013-252853 A, a difference between the traveling in the CD mode and the traveling in the CS mode is realized by an opportunity of the EV traveling being changed between the CD mode and the CS mode. In other words, in the hybrid vehicle described above, the threshold of the power for starting the engine is higher in the CD mode than in the CS mode so that the opportunity of the EV traveling is expanded in the CD mode. In this manner, the difference between the traveling in the CD mode and the traveling in the CS mode is realized.
Power electronics technology has developed to improve performances of motors, inverters, electric power storage devices, and the like and enable an increase in motor output. Because of this technical background and a variety of driving force sources (engine and motor) to choose from for the hybrid vehicle, the realization of a special traveling with a high level of user satisfaction has been desired, in the CD mode in particular, with regard to the hybrid vehicle that has the CD mode and the CS mode.
It is conceivable that driving force characteristics of the vehicle are changed between the CD mode and the CS mode for the realization of the special traveling in the CD mode. Specifically, it is conceivable that the driving force characteristics are changed between the CD mode and the CS mode such that a vehicle driving torque with respect to the same vehicle speed and the same accelerator opening degree is higher in the CD mode than in the CS mode. In this manner, an acceleration performance of the EV traveling in the CD mode is improved, and a strong sense of acceleration can be obtained during the EV traveling while the opportunity of the EV traveling is expanded in the CD mode. However, the change in the driving force characteristics associated with the switching between the CD mode and the CS mode might be uncomfortable for the user.